Magnetizer for electrical machines

ABSTRACT

The present invention relates a device for magnetizing a rotor of an electrical machine with a power rating of at least 1 MW, wherein the rotor comprises permanent magnet material, said device comprising a yoke with an electromagnetic coil arranged to produce a pulsed magnetic field for magnetizing the permanent magnet material, wherein the magnetic field is sufficient to magnetize a permanent magnetic pole wherein the rotor and yoke is in a fixed relation to each other. The invention also relates to a method for magnetization of a rotor with permanent magnets for an electrical machine.

FIELD OF THE INVENTION

The present invention relates to an apparatus for magnetizing permanentmagnet material in a rotor, the invention further relates to a methodfor magnetizing permanent magnet material in a rotor.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In general the use of electrical machine, and also for wind turbinescomprises use of one of at least two basic types of generators i.e.generators based on electromagnetism or permanent magnets respectively.The present invention relates to a magnetizer for magnetizing agenerator comprising permanent magnets (PM). The invention is notlimited to electrical generators or machine in wind turbines; it appliesto all other applications as well.

PM generators comprises two components i.e. a rotating magnetic fieldconstructed using permanent magnets, known as the rotor and a stationaryarmature constructed using electrical windings located in a slotted ironcore, known as the stator.

In magnetized condition said permanent magnets have a North-seeking poleand a South-seeking pole respectively. Opposite pole types attract,while poles of the same type repel each other. Furthermore poles ofeither type attract iron, steel and a few other metals such as nickeland cobalt. All of which is considered common knowledge of the personskilled in the art.

Permanent magnets are made of ferro- (or ferri-) magnetic material suchas NdFeB, SiFe, SrFeO or the like. During the formation of the magneticmaterial, very small atomic groups called magnetic domains act as onemagnetic unit and produces a magnetic moment. The same domains alignthemselves in the same direction over a small volume. In non-magnetizedcondition the plurality of domains of said permanent magnet areorganized in a non-aligned way whereby they in a larger scale aresubstantially cancelling out each other resulting in no or a weakoverall magnetic field.

By magnetizing a ferromagnetic permanent magnet e.g. by placing it in anexternal magnetic field such as produced in a solenoid with a directcurrent passing through it, all domains tend to align with the externalmagnetic field. Some domains align more easily than others so theresulting magnetic moment depends on the strength of the appliedmagnetic fields, increasing until all possible domains are aligned.

If a ferromagnetic material is exposed for temperatures above itsspecific Curie temperature it loses its characteristic magnetic abilityas thermal fluctuations destroy the alignment of said domains.

Usually permanent magnets are substantially non magnetic when they areproduced but must be magnetized later on, e.g. on the location ofproduction, just before they are assembled or after they as componentsare built into e.g. generators. This invention relates to an idea wherethe rotor is being equipped with not magnetic permanent magnet material.

In a first aspect, the present invention relates to a device formagnetizing a rotor of an electrical machine with a power rating of atleast 1 MW, wherein the rotor comprises permanent magnet material, saiddevice comprising a yoke with an electromagnetic coil arranged toproduce a pulsed magnetic field for magnetizing the permanent magnetmaterial, wherein the magnetic field is sufficient to magnetize apermanent magnetic pole wherein the rotor and yoke is in a fixedrelation to each other.

Each of the magnetic poles includes one or more permanent magnets thateach is composed of a permanent magnetic material susceptible to beingpermanently magnetized by a strong pulsed magnetic field and, oncemagnetized, capable of generating a high electromagnetic field. When thepermanent magnetic material is produced, atomic groups in small volumesare mutually aligned with a shared polarization direction known asmagnetic domains in to produce magnetic moments.

To magnetize a pole of an electrical machine with a size bigger than 1MW requires that the magnetic field covers an area equal to the pole orsimilar, and the flux density within the covered area needs at the sametime to be nearly homogeneous, if not, the permanent magnet material isnot utilized properly.

The large magnetic field is made with magnetizer yoke, made of laminatediron sheet or other material known in the field of laminatedtransformers or electrical machines. In the yoke there are a number ofslots for receiving a coil of electrical windings. The coil is connectedto a power supply which supplies the electrical energy to produce themagnetic field.

According to one embodiment of the invention the rotor is displaced inthe radial direction before magnetizing a further permanent magneticpole.

After magnetizing one magnetic pole the shaft of the rotor is rotated toalign the rotor and the yoke for magnetizing the next magnetic pole.

According to one embodiment of the invention the ratio between thelength of the at least one permanent magnetic pole and the length of theyoke is less than or equal to one.

An advantage of the present embodiment is that the manufacturing time isreduced since the magnetization process is one pulse per magnetic pole,since the physical length of the rotor lamination and the permanentmagnet material is shorter than the length of the lamination of theyoke. Another advantage is that the magnetization bench do not need tohave a system to move the rotor in the axial direction in relation tothe yoke.

According to one embodiment of the invention the ratio between thelength of the at least one permanent magnetic pole and the length of theyoke is between one and two, and wherein the rotor is displaced in theaxial direction of the rotor between a first and a second magneticpulse.

An advantage of the present embodiment is that the magnetizer can bedesigned to handle machine with rotors of various length, a rotor for amachine with a rating of 1 MW may have a length where one pulse canmagnetize a pole, whereas a rotor with a rating of 2 MW with the samerotor diameter can be magnetized with 2 pulses.

According to one embodiment of the invention the yoke comprises arecessed area, wherein the recessed area is shaped to receive an angularsection of the rotor.

An advantage of the present embodiment is that the air gap between theyoke and the rotor core is minimized. The size of the angular sectionshould cover at least one magnetic pole.

According to one embodiment of the invention the device furthercomprises a rotor nest arranged on top of the yoke.

Advantages of present and previous claims are that there is no or verylittle air gap between yoke and rotor, and thus the magnetic energyneeded to magnetize the magnetic pole is reduced. A further advantage isthat the nest protects the surface of the rotor core against mechanicalstresses during magnetization, especially during the pulsation of themagnetic field.

The rotor nest is for protection of the rotor during the magnetization,where large magnetic force applies to both the yoke and the rotor. Thenest also ensures a specific air gap during the magnetization.

According to one embodiment of the invention the device furthercomprises a cooling arrangement for cooling the yoke.

An advantage of the present embodiment is that during the magnetizationlarge amount of energy is dissipated into the coil in order to producehigh magnetic fields in pulses. This will cause losses in the systemthat again will heat up the yoke. In order to be able to run the devicefrequently, a cooling system for the yoke is important.

According to one embodiment of the invention the device furthercomprising a power supply to provide electrical energy to theelectromagnetic coil in the yoke to generate a magnetic field in ordermagnetize the permanent magnetic material.

An advantage of the present embodiment is that the magnetizer can supplythe energy to produce the magnetic field. The energy may be stored incharged capacitors and the discharge is controlled by electronicswitches.

According to one embodiment of the invention the device furthercomprises a clamp for maintaining the rotor in a fixed relation inrespect to the yoke during magnetization.

According to one embodiment of the invention the device furthercomprising an indexer to rotate the rotor around a shaft of the rotor,the indexer is arranged to ensure that the magnetic material in therotor is positioned in respect to the yoke.

An advantage of the present embodiment is that the indexer ensures therotor with magnet assembly to proper positions for magnetization. To getan optimal magnetization of the PM material, the rotor with magnetassembly needs to be at the right position, i.e. the PM material shouldbe aligned with the yoke. The indexer supports the rotor shaft, and maylock into existing rotor shaft Key Slot.

According to one embodiment of the invention the device furthercomprising an upper yoke with an second electromagnetic coil arranged toproduce a pulsed magnetic field for magnetizing the permanent magnetmaterial, wherein the magnetic field is sufficient to magnetize a secondpermanent magnetic pole, wherein the rotor and second yoke is in a fixedrelation to each other.

According to one embodiment of the invention the yoke and the upper yokeis arranged so that the yoke and the upper yoke are arranged formagnetizing a permanent magnetic pole while the rotor and yokes are in afixed relation to each other.

An advantage of the present embodiment is that the length of the upperyoke is so that a magnetic field provided by the upper yoke is suitablefor magnetizing a magnetic pole, of a rotor with a given length, in asingle pulse, and wherein the yoke has a length so that a magnetic fieldprovided by the yoke is suitable for magnetizing a magnetic pole, ofrotor with another length, in a single pulse.

The two yoke may share the power supply, or each may have its own powersupply.

According to an embodiment of the invention the electrical machine is anelectrical generator of a wind turbine.

In a second aspect, the present invention relates a method formagnetizing a rotor of an electrical machine with a power rating of atleast 1 MW, wherein the rotor comprises permanent magnet material, saidmethod comprising the step of

-   -   arranging the rotor in respect to a yoke in a fixed relation to        each other, wherein the yoke has an electromagnetic coil        arranged to produce a pulsed magnetic field,    -   pulsing the magnetic field for magnetizing the permanent magnet        material, wherein the magnetic field is sufficient to magnetize        a permanent magnetic pole.

The advantages of the second aspect are equivalent to the advantages forthe first aspect of the present invention.

In a third aspect, the present invention relates to a control system tooperate the device for magnetizing a rotor according to any of the abovementioned embodiments in order for the device to carry out the method ofthe second aspect in an automated manner.

An advantage of the present aspect is that the control system ensures auniform magnetization of the electrical machines. This relates both frompole to pole, but also between machines. The control system can alsorecord and log manufacturing data for each machine for further use.

In a fourth aspect, the present invention relates to a device formagnetizing and assembling an electrical machine comprising a stator anda rotor with a least one permanent magnet, the device comprising amagnetizer unit for magnetizing the at least one permanent magnet of therotor, a rotor load unit and a translation unit for translating therotor from the magnetizer unit to a rotor load unit for inserting therotor into the stator.

An advantage of the present embodiment is that the device can handle thekey components of the electrical machine while the magnets aremagnetized.

According to an embodiment of the invention the translation unitcomprises a rotor flip assembly and a rotor flip drive arranged to pivotthe rotor flip assembly from a first position to a second position.

An advantage of the present embodiment is that the rotor flip assemblyis arranged to move the rotor from the magnetizer unit to a rotor loadunit in a part of a circular trajectory when the rotor flip assembly ispivoted by the rotor flip drive. When the magnets are magnetized or“alive” the forces needed to keep them away from magnetic material istremendous, thus when moving the rotor it is important to move the rotorby means of handling tool with limited degrees of freedom, by using apivoting arm only one degree of freedom has to be controlled.

According to an embodiment of the invention the rotor flip assemblycomprises a rotor flip arm arranged to provide a down force on the rotorto keep the rotor in position in respect to the magnetizer unit duringmagnetization.

An advantage of the present embodiment is that the down force maintainsdirect contact between the surface of the magnetizer and the rotor core.

According to an embodiment of the invention the rotor load unitcomprises a stator fixture for receiving the stator of the electricalmachine and a first and a second fixture to receive and fixate a shaftof the rotor at a first and a second end of the shaft, the statorfixture is arranged to move linearly in respect to the rotor therebymoving the stator linearly and inserting the rotor into the stator.

An advantage of the present embodiment is that stator moves and therotor is fixed. During the insertion of the rotor it is extremelyimportant that the stator and the rotor only can move in relation toeach other in the axial direction. When the permanent magnet material ismagnetized, known as “live magnets”, there is a high magnetic force thewill try to attract magnetic material. If there is any movement in theother directions than the axial direction a risk of direct contactbetween rotor and stator exists.

According to an embodiment of the invention the rotor load unitcomprises a stator fixture for receiving the stator of the electricalmachine, and a rotor platform with a first and a second fixture toreceive and fixate a shaft of the rotor at a first and a second end ofthe shaft, the rotor platform is arranged to move linearly in respect tothe stator fixture thereby moving the rotor linearly and positioning thestator in relation to the rotor.

An advantage of the present embodiment is that rotor moves and thestator is fixed.

According to an embodiment of the invention a first and a second fixtureis arranged to move linearly independently of each other to engage withthe shaft of the rotor.

An advantage of the present embodiment is that the first and secondfixture can move independently of each other, thus they can move apartbefore the rotor is received, when the rotor is aligned by the flip armthe first and second fixtures can move together and the rotor shaft isfixed in between the fixtures. After the fixation of the rotor the firstand second fixtures will move together to maintain the fixation of therotor.

According to an embodiment of the invention the rotor flip assembly ismounted on a displacement track to move the rotor flip assembly parallelto the rotor shaft (21).

According to an embodiment of the invention the magnetizer unit ismounted on a displacement track to move the magnetizer unit parallel tothe rotor shaft (21).

An advantage of the present and previous embodiment is that rotor can bedisplaced in respect to the yoke of the magnetizer.

According to an embodiment of the invention the rotor flip assemblymoves the rotor from a first position to a second position betweenmagnetization pulses.

An advantage of the present embodiment is that rotor can be displaced inrespect to the yoke of the magnetizer, thus the rotor core can be longerthan the laminated rotor core, and still magnetize a magnetic pole ofthe rotor by use of two magnetic pulses.

In a fifth aspect, the present invention relates a method formagnetizing and assembling an electrical machine comprising a stator anda rotor with a least one permanent magnet at a magnetizing unit,comprising a magnetizer unit for magnetizing the at least one permanentmagnet of the rotor, a rotor load unit and a translation unit fortranslating the rotor from the magnetizer unit to a rotor load unit forinserting the rotor into the stator, the method comprising the step of

-   -   magnetization of the at least one permanent magnet in the rotor,        with the magnetizer yoke assembly,    -   translating the magnetized rotor from the magnetizer yoke        assembly to the rotor insert unit with the translation unit,    -   inserting the rotor into a stator of the electrical machine with        the load unit.

According to an embodiment of the invention the step of translating themagnetized rotor is performed by the translation unit by pivoting therotor flip assembly, with rotational forces from a rotor flip drive,from a first position to a second position.

According to an embodiment of the invention the step of magnetization,the rotor flip assembly provides a down force on the rotor to keep therotor in position in respect to the magnetizer unit by means of a rotorflip arm.

According to an embodiment of the invention the step of insertingcomprises:

-   -   the rotor load unit receiving the stator of the electrical        machine at a stator fixture    -   the rotor load unit fixating a shaft of the rotor at a first and        a second end of the shaft at a first and a second fixture,    -   the stator fixture moving linearly in respect to the rotor        thereby moving the stator linearly and inserting the rotor into        the stator.

According to an embodiment of the invention the step of insertingcomprises:

-   -   rotor load unit receiving the stator of the electrical machine        at a stator fixture    -   rotor load unit fixating a shaft of the rotor at a first and a        second end of the shaft at a first and a second fixture,    -   the first and a second fixture moving linearly in respect to the        stator fixture thereby moving the rotor linearly and positioning        the stator in relation to the rotor.

The advantages of the fifth aspect are equivalent to the advantages forthe fourth aspect of the present invention.

Many of the attendant features will be more readily appreciated as thesame become better understood by reference to the following detaileddescription considered in connection with the accompanying drawings. Thepreferred features may be combined as appropriate, as would be apparentto a skilled person, and may be combined with any of the aspects of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a complete magnetizer and rotor load unit according anaspect on the invention.

FIG. 2 shows an end view of the rotor laying on the yoke, the rotor isaligned with yoke, the Figure only shows an angular section of therotor.

FIG. 3 shows a disassembled yoke with many of the key features.

FIG. 4 shows the device with a rotor on the yoke hold by the clamp andwith the flip attached to each ends of the rotor shaft.

FIG. 5 shows a rotor pivoting from the magnetizer yoke to the rotor loadunit.

FIG. 6 shows a rotor at the rotor load unit without the rotor loadfixtures engaged at the end of the rotor, the flip arms still carriesthe rotor.

FIG. 7 shows a rotor engaged at the rotor load fixtures, ready to beinserted into a stator housing. The rotor flip arm is ready to receive anew rotor at the magnetizer.

FIG. 8 shows a side view of the magnetizer with a rotor placed on theyoke, the length of the rotor lamination is equal or less than thelength of the yoke lamination.

FIG. 9 shows a side view of the magnetizer with a rotor placed on theyoke, the length of the rotor lamination is larger than the length ofthe yoke lamination. The rotor is at a first position.

FIG. 10 shows a side view of the magnetizer with a rotor placed on theyoke, the length of the rotor lamination is larger than the length ofthe yoke lamination. The rotor is at a second position.

FIG. 11 shows a flow chart of a method for magnetizing a rotor of anelectrical machine with a power rating of at least 1 MW, where the rotorcomprises permanent magnet material, according to the invention.

FIG. 12 shows a system according to the invention where magnetizer yokeassembly 101 is a sub part of the magnetization system 100.

FIG. 13 shows a flow chart of a method for magnetizing and assembling arotor of an electrical machine with a power rating of at least 1 MW,where the rotor comprises permanent magnet material, according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be explained in further details. Whilethe invention is susceptible to various modifications and alternativeforms, specific embodiments have been disclosed by way of examples. Itshould be understood, however, that the invention is not intended to belimited to the particular forms disclosed. Rather, the invention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

In general the use of electrical machine, and also for wind turbines,comprises use of one of at least two basic types of generators i.e.generators based on electromagnetism or permanent magnets 22respectively (see FIG. 2). The present invention relates to a magnetizerfor magnetizing a generator comprising permanent magnets (PM) 22. Theinvention is not limited to electrical generators or machine in windturbines; it applies to all other applications as well.

PM generators comprises two components i.e. a rotating magnetic fieldconstructed using permanent magnets 22, known as the rotor 20 and astationary armature constructed using electrical windings located in aslotted iron core, known as the stator.

In magnetized condition said permanent magnets 22 have a North-seekingpole and a South-seeking pole respectively. Opposite pole types attract,while poles of the same type repel each other. Furthermore poles ofeither type attract iron, steel and a few other metals such as nickeland cobalt. All of which is considered common knowledge of the personskilled in the art.

Permanent magnets 22 are made of ferro- (or ferri-) magnetic materialsuch as NdFeB, SiFe, SrFeO or the like. During the formation of themagnetic material, very small atomic groups called magnetic domains actas one magnetic unit and produces a magnetic moment. The same domainsalign themselves in the same direction over a small volume. Innon-magnetized condition the plurality domains of said permanent magnetare organized in a non-aligned way whereby the in a larger scale aresubstantially cancelling out each other resulting in no or a weakoverall magnetic field.

By magnetizing a ferromagnetic permanent magnet e.g. by placing it in anexternal magnetic field such as produced in a solenoid 1 with a directcurrent passing through it, all domains tend to align with the externalmagnetic field. Some domains align more easily than others so theresulting magnetic moment depends how strong the applied magnetic fieldsis, increasing until all possible domains are aligned.

If a ferromagnetic material is exposed for temperatures above itsspecific Curie temperature it loses its characteristic magnetic abilityas thermal fluctuations destroy the alignment of said domains.

Usually permanent magnets 22 are substantially not magnetic when theyare produced but must be magnetized later on, e.g. on the location ofproduction, just before they are assembled or after they as componentsare built into e.g. generators. This invention relates an idea where therotor is being equipped with not magnetic permanent magnet material.

In a first aspect, the present invention relates to a device formagnetizing a rotor of an electrical machine with a power rating of atleast 1 MW, wherein the rotor 20 comprises permanent magnet material,the magnetization device 101 comprising a yoke or lamination core 2 withan electromagnetic coil 1 arranged to produce a pulsed magnetic fieldfor magnetizing the permanent magnet material, wherein the magneticfield is sufficient to magnetize a permanent magnetic pole 23 whereinthe rotor 20 and laminated core or yoke 2 is in a fixed relation to eachother.

Each of the magnetic poles 23 includes one or more permanent magnets 22that each composed of a permanent magnetic material susceptible to beingpermanently magnetized by a strong pulsed magnetic field and, oncemagnetized, capable of generating a high electromagnetic field. When thepermanent magnetic material is produced, atomic groups in small volumesare mutually aligned with a shared polarization direction known asmagnetic domains in to produce magnetic moments.

To magnetize a magnetic pole 23 of an electrical machine with a sizebigger than 1 MW requires that the magnetic field covers an area equalto the pole or similar. The flux density within the covered area needsat the same time to be nearly homogeneous, if not, the permanent magnetmaterial is not utilized properly.

The large magnetic field is made with magnetizer yoke, made of laminatediron/steel sheets or other material known in field of laminatedtransformers or electrical machines. In the yoke 2 there are a number ofslots for receiving a coil 1 of electrical windings. The coil 1 isconnected to a power supply 13 which supplies the electrical energy toproduce the magnetic field.

FIG. 1 shows a magnetizing and machine assembly for insertion of therotor 20 into the stator 25 including handling equipment 31 for handlingthe rotor 20 with magnetized permanent magnets 22. The figure shows thecomponent mounted on a system base 50, with a rotor located at themagnetizer yoke assembly 101, the shaft 21 of the rotor is attached to arotary indexer 14, the yoke assembly 101 is fed with electrical energythrough cables in a cable conduit 9, and the electrical energy issupplied from a power supply 13. The rotor 20 is kept in a fixedrelation to the yoke 2, by a rotor flip arm 31 that can grip the ends ofthe shaft 21, in addition there is a machine clamp 34 to keep the rotorin place. The machine clamp 34 provides a down force on the rotor core20 during magnetization.

According to an embodiment of the invention the rotor flip assembly 30comprises a rotor flip arm 31 arranged to provide a down force on therotor to keep the rotor in position in respect to the magnetizer unitduring magnetization. The down force maintains direct contact ormaintains an air gap between the surface of the magnetizer and the rotorcore 20.

According to an embodiment of the invention as seen in FIG. 7, themagnetizer unit is mounted on a displacement track 36 to move themagnetizer unit 101 parallel to the rotor shaft 21.

In one embodiment, the power supply 13 (see FIG. 1) includes a bank ofcapacitors, a switching device connecting the capacitor bank with theleads of the coil 1, a charging circuit configured to charge thecapacitor bank, and a control system 80 (not shown in the Figures). Thecontrol circuit is configured to activate the charging circuit to chargethe capacitor bank and is also configured to actuate the switchingdevice to abruptly discharge the stored charge from capacitor bank as atransient high-voltage direct current pulse through the coil 1. Theswitching device may be, for example, a silicon controlled rectifier.The stored charge released from the capacitor bank generates the directcurrent pulse in the turns of the coil 1, which in turn generates therelatively strong magnetic field of short duration (typically a fewmilliseconds) used to magnetize each magnetic pole 23. As the directcurrent pulse in the coil 1 dissipates, the external magnetic fieldcollapses. The control circuit can cause the capacitor bank andswitching device to output direct current pulses to the coil 1 withcurrent flow in either a clockwise direction or a counter clockwisedirection to produce a magnetic field of two different polaritiesaccording to Faraday's Law. In an alternative embodiment, the chargingcircuit may be a different type of circuit capable of producing a signalhaving a current level and a rate change of current adequate to generatethe requisite direct current pulses.

The power supply 13 is then used to magnetize the permanent magnets 22constituting the pole 23. The control circuit 80 of power supply 13 isoperated to activate the charging circuit to charge the capacitor bank.When sufficiently charged, the control circuit actuates the switchingdevice of power supply 13 to abruptly discharge the stored charge fromcapacitor bank as a first current pulse through the coil 1 in a, forexample, clockwise direction. The passage of the first current pulsethrough the coil 1 generates a magnetic field.

After the rotor 20 is fully magnetized it is ready to be inserted intothe stator 25. In order to transfer the rotor 20 safe from themagnetizer 101 to the rotor load unit 60 a rotor flip assembly 30 isused. The rotor flip assembly can be seen in FIG. 7, where the rotorflip arms 31 are empty. The rotor flip arms are mounted to a flip shaft32 that can rotate and thus pivot a rotor from the magnetizer 101 to therotor load unit 60. The shaft rotates by a flip drive 35, which can becontrolled by an automated control system 80. The rotor flip arms 31 hasa shaft lock 40 attached to each of the arms. The shaft locks 40 locksthe rotor shaft 21 and maintain the rotor shaft in the recessed area 42of the rotor flip arm 31.

An advantage of the present embodiment is that the device can handle thekey components of the electrical machine while the magnets aremagnetized. According to an embodiment of the invention the translationunit comprises a rotor flip assembly and a rotor flip drive arranged topivot the rotor flip assembly 30 from a first position to a secondposition. An advantage of the present embodiment is that the rotor flipassembly 30 is arranged to move the rotor from the magnetizer unit in apart of a circular trajectory when the rotor flip assembly is pivoted bythe rotor flip drive. When the magnets are magnetized or “alive” theforces needed to keep them away from magnetic material, such as ironetc. is tremendous, thus when moving the rotor 20 it is important tomove it by means of handling tool with limited degrees of freedom, byusing a pivoting arm 31 only one degree of freedom has to be controlledby the automated control system 80.

In an embodiment of the present invention the rotor flip assembly 30moves the magnetized rotor from the magnetizer 101 to the rotor loadunit 60 by means of a robotic manipulator, wherein the move is handledin a combination of rotational and linear paths.

In an embodiment of the present invention the rotor flip assembly 30moves the magnetized rotor from the magnetizer 101 to the rotor loadunit 60 by means of vehicle, where the magnetized rotor is placed ontothe vehicle (not shown) and moved to the rotor load unit 60 where therotor is placed in the rotor load unit 60.

According to an embodiment of the invention the rotor flip assembly ismounted on a displacement track 33 to move the rotor flip assembly 30parallel to the rotor shaft 21. The movement of the rotor flip assemblyis important when magnetizing magnetic pole 23 in rotors 20 longer thanthe yoke 2, as seen in FIG. 9. According to one embodiment of theinvention the rotor is displaced in the radial direction beforemagnetizing a further permanent magnetic pole.

According to one embodiment of the invention the ratio between thelength of the at least one permanent magnetic pole and the length of theyoke is less than or equal to one, this is what is shown in FIG. 8 wherethe length of the rotor core 20 fits the length of the magnetizer yoke2. An advantage of this is that the manufacturing time is reduced, sincethe magnetization process is one pulse per magnetic pole, since thephysical length of the rotor lamination and the permanent magnetmaterial is shorter than or equal the length of the lamination of theyoke. Another advantage is that the magnetization bench do not need tohave a system 33 to move the rotor in the axial direction in relation tothe yoke.

According to one embodiment of the invention the ratio between thelength of the at least one permanent magnetic pole and the length of theyoke is between one and two, and wherein the rotor is displaced in theaxial direction of the rotor between a first and a second magneticpulse. This means that either the rotor 20 is moved by the rotor flipassembly 30 or the magnetizer yoke assembly 101 is moved. The firstposition is shown in FIG. 9 and the second is shown in FIG. 10, oropposite. An advantage of present embodiment is that the magnetizer canbe designed to handle machine with rotors of various length, a rotor fora machine with a rating of 1 MW may have a length where one pulse canmagnetize a pole, whereas a rotor with a rating of 2 MW with the samerotor diameter can be magnetized with 2 pulses.

FIG. 2 shows an end view of the magnetizer yoke 2, with a cut outsection of a rotor 20 for magnetization. Each of the magnetic poles 23includes one or more permanent magnets 22 that are each composed of apermanent magnetic material susceptible to being permanently magnetizedby a strong magnetic field and, once magnetized, capable of generating ahigh electromagnetic field. The actual magnetization occurs when a shorthigh current pulse flows through the coil 1 in the yoke 2. Thisgenerates a high magnetic field and the magnetic material in themagnetic pole 23 is magnetized. Depending on the physical length of theyoke 2 and the length of the rotor core 20, one or two pulses are neededto magnetize the magnetic pole 23 in the full length. After one magneticpole has been magnetized any forces, applied on the rotor 20 by the fliparm 31 and the machine clamp 34, are released. The rotary indexer 14(see FIG. 1) can rotate the rotor 20 to align it with the non magneticpermanent magnetic material becoming the adjacent magnetic pole 23 whenmagnetized. This process is continued until the rotor 20 is fullymagnetized.

The indexer 14 (see FIG. 1) ensures the rotor with magnet assembly inproper positions for magnetization. To get an optimal magnetization ofthe PM material, the rotor with magnet assembly needs to be at the rightposition, i.e. the PM material should be aligned with the yoke 2. Theindexer 14 (see FIG. 1) supports the rotor shaft 21, and may lock intoexisting rotor shaft Key Slot (not shown).

When the permanent magnetic material is produced, atomic groups in smallvolumes are mutually aligned with a shared polarization direction knownas magnetic domains in to produce magnetic moments. In a non-magnetizedcondition, the various domains of the permanent magnetic material ineach permanent magnet 22 are organized with different alignments suchthat, on a larger scale, the magnetic moments effectively cancel eachother resulting in no net magnetic field or a weak overall magneticfield. All domains tend to align with an external magnetic field inorder to magnetize the magnetic material. Some domains align more easilythan others so the resulting magnetic field of the magnetized permanentmagnet 22 is dependent upon the strength of the applied externalmagnetic field.

In one embodiment, each permanent magnet 22 is a rare-earth magnetcontaining a permanent magnetic material composed of an alloy containingone or more rare earth (lanthanide) elements, such as neodymium orsamarium, that are ferromagnetic metals. Certain alloys containing rareearth elements and transition metals, such as iron, nickel, or cobalt,have a Curie temperature far above room temperature, which is adesirable property for the permanent magnets 22. Representative alloyssuitable for the permanent magnetic material of permanent magnets 22include, but are not limited to, a samarium alloy containing cobalt(SmCo₅) and a neodymium alloy containing iron and boron (Nd₂Fe₁₄B). Aplating layer or coating may be applied to protect the permanent magnets22 against corrosion, breakage, and chipping. Rare earth alloys arecharacterized by a crystalline structure of large magnetic anisotropythat promotes magnetization in one particular direction by a strongmagnetic field but, once magnetized, is resistant to being magnetized inany different direction. The permanent magnetization may be altered byintentionally applying a magnetic field that is intended to demagnetizethe permanent magnetic material.

In an embodiment of an electrical machine, each magnetic pole 23includes multiple individual permanent magnets 22 that are adhesivelybonded to an outer surface of the rotor frame or joined thereto usingmechanical clips, frames, or other conventional mechanical fasteningtechniques to form each magnetic pole 23. Alternatively, instead ofmultiple magnets 54, each of the magnetic poles 23 may be constituted bya single, unitary permanent magnet 22 of a monolithic construction.

In alternative embodiments, the permanent magnetic material in thepermanent magnets 22 may be a ceramic or ferrite material, or alnico.However, rare earth alloys are preferred for the permanent magnets 22because of a comparatively higher remanence (B_(r)) that is related tomagnetic field strength, a comparatively higher coercivity (H_(ci)) thatgauges resistance to demagnetization, and a comparatively higher energyproduct (BH_(max)) that is related to energy density.

The permanent magnets 22 are illustrated as having the shape ofrectangular blocks that, if multiple permanent magnets 22 are present ineach magnetic pole 23, have an end-to-end arrangement. However, eachpermanent magnet 22 is not constrained to have a rectangular blockshape. The permanent magnets 22 also have a slight curvature to conformto the shape of the outer surface of the rotor frame, if mounted on thesurface instead of being embedded in the rotor core 20. Themagnetization system 100 (see FIG. 1) generates a strong or highintensity magnetic field of short duration that is used to magnetize themagnetic material in the permanent magnets 22 of the magnetic poles 23.The magnetization system 100 (see FIG. 1) generates the magnetic fieldby causing a transient high current pulse to be directed from the powersupply 13 (see FIG. 1) through the turns of the coil 1 of magnetizeryoke assembly 101 (see FIG. 3). The discrete magnetic fields generatedby the individual turns of the coil 1 constructively add to yield thetotal magnetic field emanating from the magnetizer yoke assembly 101when the coil 1 is energized. The magnetic field generated by the coil 1generally scales with increasing current level of the current pulse andwith the number of turns in the coil 1.

FIG. 3 shows a detailed view of the magnetizer yoke assembly 101. Theheart of the system is the coil 1 in which a current from the powersupply 13 (see FIG. 1) can flow and then cause a magnetic flux formagnetization of permanent magnet material. The coil 1 is embedded inslots in a laminated core 2, an end block 7 a, 7 b is placed at bothends of the laminated core 2, and the core is terminated by a clampplate 8 a, 8 b also at both ends. All the parts of the core are tiedtogether by tie rods 12. On top of the coils in the slot, top sticks 11are placed to protect the coil 1. According to one embodiment of theinvention the yoke comprises a recessed area, wherein the recessed areais shaped to receive an angular section of the rotor. The air gapbetween the yoke and the rotor core is therefore minimized. The size ofthe angular section should cover at least one magnetic pole 23.

In the embodiment, a rotor nest 3 is placed on top of the yoke assembly101. The rotor nest is to protect the rotor core 20, but also to ensurea well defined air gap between the rotor core and the laminated core 2.There is no or very little air gap between yoke and rotor, and thus themagnetic energy needed to magnetize the magnetic pole is reduced. In anembodiment the nest 3 is made of a soft flexible material that isdeformable in order to protect the rotor core 20. In one embodiment thenest is made of a material that conducts the magnetic flux from thelaminated core of the yoke 2 to the rotor core 20. An advantage is thatthe nest 3 protects the surface of the rotor core against mechanicalstresses during magnetization, especially during the pulsation of themagnetic field, where large magnetic force applies to both the yoke andthe rotor.

The coil is connected to the power supply 13 through a cable assembly 4.The cable assembly is placed in a cable conduit 9.

In order to keep the core 2 at a preferred operating temperature thecore is placed on a cold plate 5. The cold plate 5 is equipped withpipes for a liquid coolant and the pipes can be attached to a liquidcooling system that will keep the temperature in the core 2. In otherembodiments the cooling system may comprise the coolant pipes embeddedin the core 2. During the magnetization large amount of energy isdissipated into the coil 1 in order to produce high magnetic fields inpulses. This will cause losses in the system that again will heat up theyoke core 2. In order to be able to run the device frequently, a coolingsystem for the yoke is important.

The cold plate 5 is placed in a support structure 6 and on top of thatthe core 2 is placed.

In one embodiment of the invention the device further comprises an upperyoke with a second electromagnetic coil arranged to produce a pulsedmagnetic field for magnetizing the permanent magnet material, whereinthe magnetic field is sufficient to magnetize a second permanentmagnetic pole, wherein the rotor and second yoke is in a fixed relationto each other. The second yoke can be located opposite the first yoke 2,so the two yokes are displaced 180 degrees around the periphery of arotor core 20. The length of the yoke may be the same or they can bedifferent. The yokes may operate so both of them can magnetize amagnetic pole 23 while the rotor is fixed. They may operate independentof each other or the may share the power supply 13. If they share thepower supply, only one yoke at the time may pulse a magnetic field.

The method for magnetizing a rotor of an electrical machine with a powerrating of at least 1 MW, where the rotor comprises permanent magnetmaterial, is shown in the flow chart 200 in FIG. 11. After the start 201the method does comprise the steps;

Step 202 is arranging the rotor 20 in respect to the yoke 2 in a fixedrelation to each other, wherein the yoke has an electromagnetic coil 1arranged to produce a pulsed magnetic field,

Step 203 is pulsing the magnetic field for magnetizing the permanentmagnet material 22, wherein the magnetic field is sufficient tomagnetize a permanent magnetic pole 23.

Whenever the rotor 20 is longer than the yoke 2, Step 204 is fordeciding whether the rotor 20 needs to be shifted (step 205) in theaxial direction, (see FIG. 9 and FIG. 10 that shows the rotor 20 in twodifferent positions), Step 206 rotates the rotor 20 to align furthermagnetic poles with yoke 2. Step 207 decides whether all magneticmaterial has been magnetized, i.e. the rotor has been rotated 360degrees. Step 208 concludes the method.

A machine with only one magnetic pole only requires the steps 202, 203and 208. FIG. 12 shows the invention where magnetizer yoke assembly 101is a sub part of the magnetization system 100. A control system 80operates the magnetizer yoke assembly and gets feedback from it. Formagnetizing a rotor 20 according to any of the mentioned embodiments inorder for the device to carry out the method in an automated manner thecontrol system executes the needed commands. An advantage of the controlsystem is that it ensures a uniform magnetization of the electricalmachines. This relates both from pole to pole, but also betweenmachines. The control system 80 can also record and log manufacturingdata for each machine for further use. The control system 80 alsocontrols whole the magnetization system 100.

The magnetisation system 100 as shown in FIG. 1 is a device formagnetizing and assembling an electrical machine with a stator and arotor 20 with a least one permanent magnet 22, the device 100 comprisinga magnetizer unit 101 for magnetizing the at least one permanent magnet22 of the rotor, a rotor load unit 60 and a translation unit 30 fortranslating the rotor 20 from the magnetizer unit to a rotor load unit60 for inserting the rotor into the stator.

In an embodiment of the invention the rotor load unit 60 comprises astator fixture 42 (see FIG. 6) for receiving the stator of theelectrical machine and a first 38 and a second fixture 39 to receive andfixate a shaft of the rotor at a first and a second end of the shaft,the stator fixture is arranged to move linearly in respect to the rotorthereby moving the stator linearly and inserting the rotor into thestator. The stator platform moves along stator displacement track 37.

FIG. 4 shows a rotor 20 at the yoke 2 the flip arm 31 are holding therotor 20 at the rotor shaft 21. The shaft lock 40 locks the rotor 20,and the main clamp 41 applies a down force on the rotor 20.

FIG. 5 shows the rotor 20 in the transition state where it is pivoted bythe rotor flip assembly 30, from the magnetizer yoke assembly to therotor load unit 60 (see FIG. 1). In FIG. 6 the rotor 20 has been pivotedall the way to the rotor load unit 60, and is ready to be fixed at thefirst and second fixtures 38 and 39. The first and second fixture 38, 39can move independently of each other, thus they can move apart beforethe rotor is received, when the rotor is aligned by the flip arm 31 thefirst and second fixtures 38, 39 can move together and the rotor shaft21 is fixed in between the fixtures. After the fixation of the rotor thefirst 38 and second fixtures 39 will move together to maintain thefixation of the rotor 20 through the shaft 21.

FIG. 7 shows the rotor 20 fixed at the first and second fixtures 38 and39. The rotor flip arms 31 have been pivoted back to the magnetizer yokeassembly 101. The rotor 20 is ready to be insert into the stator housing25 (see FIG. 1). The stator housing 25 moves along the load unitdisplacement tracks 37, until the rotor is fully enclosed in the statorhousing. The rotor is fixed in the stator housing by locking the machineend shield 44 to the stator housing 25.

During the insertion of the rotor it is extremely important that thestator and the rotor only can move in relation to each other in theaxial direction. When the permanent magnet material is magnetized, knownas “live magnets”, there is a high magnetic force the will try toattract magnetic material. If there is any movement in the otherdirections than the axial direction a risk of direct contact betweenrotor and stator exists.

In another embodiment of the invention the rotor load unit comprises astator fixture for receiving the stator of the electrical machine, and arotor platform with a first and a second fixture 38, 39 to receive andfixate a shaft of the rotor at a first and a second end of the shaft 21,the rotor platform is arranged to move linearly in respect to the statorfixture thereby moving the rotor linearly and positioning the stator inrelation to the rotor. An advantage of the present embodiment is thatrotor moves and the stator is fixed.

The method for magnetizing and assembling an electrical machinecomprising a stator and a rotor with a least one permanent magnet at amagnetizing unit 101, comprising a magnetizer unit for magnetizing theat least one permanent magnet 22 of the rotor 20, a rotor load unit 60and a translation unit 30 for translating the rotor 20 from themagnetizer unit 101 to a rotor load unit 60 for inserting the rotor 20into the stator 25, the method 300 is shown in FIG. 13. The method 300starts in step 301. the magnetization of the at least one permanentmagnet 22 in the rotor 20, with the magnetizer yoke assembly 101 is step302. Step 303 is translating the magnetized rotor from the magnetizeryoke assembly to the rotor insert unit with the translation unit, andstep 304 is inserting the rotor into a stator of the electrical machinewith the load unit.

In an embodiment the step 303 of translating the magnetized rotor isperformed by the translation unit by pivoting the rotor flip assembly30, with rotational forces from a rotor flip drive 35, from a firstposition to a second position.

According to an embodiment of the invention the step of magnetization,the rotor flip assembly 30 provides a down force on the rotor to keepthe rotor in position in respect to the magnetizer unit by means of arotor flip arm 31.

In an embodiment of the step 304 of inserting comprises, the rotor loadunit 60 receiving the stator 25 of the electrical machine at a statorfixture 42, the rotor load unit 60 fixating a shaft of the rotor 20 at afirst and a second end of the shaft 21 at a first and a second fixture38, 39, the stator fixture 42 moving linearly in respect to the rotorthereby moving the stator linearly and inserting the rotor into thestator.

In another embodiment of the invention the step 304 of insertingcomprises: the rotor load unit 60 receives the stator 25 of theelectrical machine at a stator fixture 42, rotor load unit 60 fixating ashaft 21 of the rotor 20 at a first and a second end of the shaft at afirst and a second fixture 38, 39, the first and a second fixture movinglinearly in respect to the stator fixture thereby moving the rotorlinearly and positioning the stator 25 in relation to the rotor 20.

Any range or device value given herein may be extended or alteredwithout losing the effect sought, as will be apparent to the skilledperson.

It will be understood that the above description of a preferredembodiment is given by way of example only and that variousmodifications may be made by those skilled in the art. The abovespecification, examples and data provide a complete description of thestructure and use of exemplary embodiments of the invention. Althoughvarious embodiments of the invention have been described above with acertain degree of particularity, or with reference to one or moreindividual embodiments, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thespirit or scope of this invention.

The invention claimed is:
 1. A device for magnetizing a rotor of an electrical machine, wherein the rotor comprises permanent magnet material, said device comprising: a yoke with an electromagnetic coil arranged to produce a pulsed magnetic field for magnetizing the permanent magnet material, wherein the magnetic field is sufficient to magnetize a permanent magnetic pole, and wherein the rotor and yoke are in a fixed relation to each other when the electromagnetic coil is producing the pulsed magnetic field; and a rotor nest arranged on the yoke, wherein the rotor nest is arranged between the yoke and the rotor.
 2. A device according to claim 1, wherein the rotor is displaced in the radial direction before magnetizing a further permanent magnetic pole.
 3. A device according to claim 2, wherein the device further comprising an indexer to rotate the rotor around a shaft of the rotor, the indexer is arranged to ensure that the magnetic material in the rotor is positioned in respect to the yoke.
 4. A device according to claim 1, wherein the ratio between the length of the at least one permanent magnetic pole and the length of the yoke is less than or equal to one.
 5. A device according to claim 1, wherein the ratio between the length of the at least one permanent magnetic pole and the length of the yoke is between one and two, and wherein the rotor is displaced in the axial direction of the rotor between a first and a second magnetic pulse.
 6. A device according to claim 1, wherein the yoke comprises a recessed area, wherein the recessed area is shaped to receive an angular section of the rotor.
 7. A device according to claim 1, wherein the device further comprises a cooling arrangement for cooling the yoke.
 8. A device according to claim 1, wherein the device further comprising a power supply to provide electrical energy to the electromagnetic coil in the yoke to generate a magnetic field in order magnetize the permanent magnetic material.
 9. A device according to claim 1, wherein the device further comprising a clamp for maintaining the rotor in a fixed relation in respect to the yoke during magnetization.
 10. A device according to claim 1, wherein the device further comprises an upper yoke with an second electromagnetic coil arranged to produce a pulsed magnetic field for magnetizing the permanent magnet material, wherein the magnetic field is sufficient to magnetize a second permanent magnetic pole; and wherein the rotor and second yoke is in a fixed relation to each other when the upper yoke is producing the pulsed magnetic field.
 11. A device according to claim 10, wherein the yoke and the upper yoke are arranged so that the yoke and the upper yoke magnetize a permanent magnetic pole while the rotor and yokes are in a fixed relation to each other.
 12. A device according to claim 1, wherein a yoke and an electromagnetic coil are mounted on a base, wherein the base includes a handling tool that holds the rotor, and wherein the handling tool is rotatable around an axis to move the rotor from a first position relative to the base to a second position relative to the base.
 13. A device according to claim 12, wherein the base further comprises a rotor load unit arranged at the second position relative to the base, wherein the rotor can be attached to the rotor load unit, and wherein the rotor load unit is displaceable relative to the base to move the attached rotor into an installed arrangement in a stator.
 14. A method for magnetizing a rotor of an electrical machine, wherein the rotor comprises permanent magnet material, said method comprising: arranging the rotor in respect to a yoke, wherein the yoke has an electromagnetic coil arranged to produce a pulsed magnetic field, wherein a rotor nest is arranged on the yoke such that the rotor nest is between the yoke and the rotor when the rotor is arranged with respect to the yoke; and pulsing the magnetic field for magnetizing the permanent magnet material, wherein the magnetic field is sufficient to magnetize a permanent magnetic pole.
 15. A method according to claim 14 further comprising displacing the rotor in the radial direction before magnetizing a further permanent magnetic pole.
 16. A method according to claim 14, wherein the ratio between the length of the at least one permanent magnetic pole and the length of the yoke is between one and two, and wherein the method further comprising the step of displacing the rotor in the axial direction between a first and a second magnetic pulse.
 17. A method according to claim 14, further comprising cooling the yoke with a cooling system.
 18. A method according to claim 14, further comprising charging an energy storage and discharging the energy in the electromagnetic coil to produce the pulsed magnetic field.
 19. A method according to claim 14, further comprising rotating the rotor around a shaft of the rotor, by means of an indexer, the indexer is arranged to ensure that the magnetic material in the rotor is positioned in respect to the yoke.
 20. A device for magnetizing a rotor of an electrical machine, said device comprising: a yoke with an electromagnetic coil arranged to produce a pulsed magnetic field, wherein said yoke includes an curvilinear surface; and a rotor nest that includes a first surface and a second surface opposite the first surface, wherein the first surface is arranged on the curvilinear surface of the yoke, and wherein the second surface of the rotor nest includes a second curvilinear surface defining a contour that is substantially similar to an outer contour of the rotor. 